The future LTE-A (Long Term Evolution Advanced) system will support a transmission bandwidth up to 100 MHz, while the maximum transmission bandwidth supportable by the LTE (Long Term Evolution) standard is 20 MHz. Thus to achieve the higher transmission bandwidth, it requires to aggregate multiple carriers. Carrier aggregation (CA) is a technique of aggregating multiple carriers for combined transmission, which is proposed by 3GPP (3rd Generation Partnership Project) to meet the high transmission bandwidth requirement of the future mobile systems. Carrier aggregation may be classified into consecutive carrier aggregation and non-consecutive aggregation based on the positions of the carriers that are aggregated on the spectrum. LTE-A will support both of the two CA scenarios. While introducing the CA technique, 3GPP also considers its backward compatibility, which means that user equipments (UEs) supporting CA and UEs not supporting CA will co-exist for a long time in the future. A CA supporting UE can be connected to a plurality of component carriers (CCs) at the same time, and a UE not supporting CA can be connected to only a certain CC.
FIGS. 1, 2, and 3 illustrate application scenarios of the present application. The 3 application scenarios as shown are preferred deployment scenarios for carrier aggregation and represent 3 typical application examples of carrier aggregation. In FIG. 1 the coverage of the cells corresponding to carriers F1 and F2 are substantially coincident, i.e. F1 and F2 provide coverage areas similar to each other. F1 and F2 may be arranged in the same carrier band, which is a typical consecutive CA scenario. FIGS. 2 and 3 each show an example of non-consecutive CA, in which F1 and F2 may be located in different carrier band. The cell corresponding to F1 is used to ensure the coverage and the cell corresponding to F2 is used to improve the throughput. The difference between FIG. 2 and FIG. 3 lies in that, in FIG. 3 the antenna of the cell corresponding to F2 is directed to the edge area of the cell corresponding to F1, therefore the application scenario of FIG. 3 can significantly improve the throughput of the edge area of the cell corresponding to F1.
To simplify the wireless resource management under CA scenarios, LTE-A introduces the concept of “primary frequency”. Accordingly, the cell corresponding to the primary frequency is referred to as a “primary cell”. When UE has a high data transmission requirement, it may enter into CA transmission mode, and thus the UE needs to be allocated with a new component carrier (CC), that is, a secondary cell needs to be provided to the UE. In the CA operation mode, in order to maintain the power consumption of the UE at a normal level, a mechanism of activating and deactivating the downlink of the secondary cell is introduced. When the secondary cell is deactivated, the UE does not receive the corresponding control channel information (PDCCH or PDSCH), and needs not to measure the channel quality. When the secondary cell is activated, the operation is the reverse, that is, the UE receives the corresponding control channel information. The activating or deactivating of the downlink of the corresponding secondary cell is decided by a control signaling (control element) in the media access control (MAC) layer transmitted by the base station, or the downlink of a secondary cell may be deactivated in an implicit manner by using a timer.
To activate the uplink of a secondary cell, the most natural processing manners including two types. One activating manner is similar to the activating of the downlink, i.e. an activating command may be explicitly transmitted to activate the uplink of the secondary cell. This explicit command can be transmitted together with the command for activating the downlink of the secondary cell. Alternatively, the uplink of the secondary cell can be activated separately when the uplink data transmission amount increases. Another uplink activating manner is an implicit manner. In other words, when the downlink of a secondary cell is activated, the uplink corresponding to this downlink is activated at the same time. In this manner, explicitly transmitting a command of activating the uplink is not needed.
The advantage of using the explicit command lies in that, for UE having only a single RF chain, the transmission bandwidth may be adjusted as the sum of bandwidths of activated cells, instead of being set as the sum of bandwidths of all the cells allocated to the UE (the number of all the cells allocated to the UE is larger than or equal to the number of the activated cells). In this way, the power consumption of the UE can be further saved. The disadvantage of using the explicit command lies in that, when the uplink of a new secondary cell is needed to be activated, the delay necessary for adjusting the RF transmission bandwidth can result in communication interrupt or data loss during the time period of the delay. In addition, the use of the explicit MAC layer control signaling may increase the amount of corresponding control information.
The advantage of using the implicit command lies in that, the amount of MAC layer control information is not increased and the process of transmitting and handling the control signaling is implied. The disadvantage of using the implicit command lies in that, for UE having only a single RF chain, the transmission bandwidth is the sum of bandwidths of all its cells, regardless of whether the secondary cell(s) is activated or not. In this way, the power consumption of the UE is increased. At the same time, the advantage thereof is that, when the uplink of a new secondary cell is activated, the transmission bandwidth needs not to be adjusted and thus no communication interrupt and data packet loss are resulted.
It is to be noted that, in the disclosure the so-called uplink and downlink may be correlated with each other based on system information block 2 (SIB2) (i.e. cell-based correlation), or may be correlated based on UE.
As can be seen from above, for UE having only a single RF chain, power consumption and communication interrupt are two key issues, which can not be solved at the same time by the above explicit command manner or by the implicit command manner.